Method and apparatus for detecting mis-stripping in a punch press machine

ABSTRACT

A method and apparatus for detecting the presence of mis-stripping uses a sensor function section free from operation sensibility variation or destruction due to vibration, impact or the like. Only a ram head in a punch press is provided in an electrically insulated state on the machine side and a low voltage is applied to the ram head. Grounding and conduction of the ram head to the machine side through punch tools is detected when the ram head is in contact with the punch tools, nonconduction is detected when the ram head and punch tools are not in contact, and the nonconduction time is determined to be mis-stripping.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus for detecting mis-stripping in a punch press machine.

[0003] 2. Description of Related Art

[0004] In the punch press processing, when continuous punching is performed, a proper stripping of punch tools is distinguished from mis-stripping, by detecting whether or not the punch tool is separated from the punched work piece, by the contact or separation between the ram head and the punch tools during the upward (return) movement of the punch tools. That is because, in mis-stripping, if the work piece is moved, damage to tools and to the work piece can result, thereby resulting in poor manufacturing.

[0005] Prior methods for detecting whether or not punch tools are in contact with the ram head, include a method of attaching a metal round bar (called an area bar) bent in U from the side to the bottom of a ram head, distinguishing electrical conduction or non conduction by contact/non contact between the area bar (ram head) and the punch tools thereby determining whether or not mis-stripping is present.

[0006] Another existing method uses an optical fiber sensor attached to the ran head, adjusting the same so that the optical axis of the sensor passes the ram head bottom, and determining the presence or absence of contact between the bottom of the ram head and the top face of the punch tool by whether or not the sensor optical axis is connected by the ram head and the punch tools, and thereby determines the present or absence of mis-stripping.

[0007] However, all of the aforementioned prior methods are embodiments wherein a means for detecting mis-stripping is attached outside the ram head or punch tools in a punch press machine by a mechanical post attachment structure. Such an arrangement is often complicated and, moreover, assembly and maintenance thereof are difficult. Problems, as mentioned above, are similar in the case when the punch press machine is a turret punch press machine.

[0008] Particularly, in the prior art, the member serving as a sensor is provided in a movable portion of the ram head or in the vicinity thereof by exterior attachment. Therefore, the sensor function member is fragile and easily susceptible to vibration or impact of the punch press machine, and the sensibility of the sensor adjusted beforehand tends to vary due to deviation of the optical axis for an optical member and the deviation of the contact position for an electric member. In addition to these inherent problems, such an arrangement can not be applied to certain forms of tools used for a punch press machine (for example, in case of wheel tool, the punch tools rotates in contact section, inhibiting such use).

[0009] In view of problems of the prior art as mentioned above, the present invention provides a method and apparatus for detecting the presence of mis-stripping in a punch press using a sensor function section free from variation due to operation or destruction due to vibration, impact or the like, by a structure housing a portion serving as a sensor in a structure of a punch press machine.

SUMMARY OF THE INVENTION

[0010] The method of the invention having an object to resolve the aforementioned problems includes providing a punch press with only a ram head thereof electrically insulated from a machine side and applying a low voltage to the ram head. The grounding and conduction of the ram head to the machine side through the punch tools is detected when the ram head is in contact with the punch tools, nonconducting is detected when the ram head and the punch tools are not in contact, and the nonconducting is judged to be mis-stripping.

[0011] The mis-stripping detection apparatus for performing the aforementioned method includes a ram and a ram head in a punch press made as a joint structure by bolting, electrical insulation between the ram and ram head at the joint portion of the ram and the ram head, and electrical insulation between the contact portion of a bolt used for joining the ram and the ram head, and wiring for applying a low voltage to the ram head. The conduction or disconnection of an electric circuit formed by the ram head including the wiring and the punch tools side is detected.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. I is a cross section of essential parts including a ram head and punch tools of a punch press machine to which a method of the present invention is applied; and

[0013]FIG. 2 is a cross section of the ram head of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0014] Next, embodiments of the present invention will be described referring to the accompanying drawings. FIG. 1 is a cross section of essential parts of the present apparatus including a ram head and punch tools of a punch press machine to which the method of the invention is applied, and FIG. 2 is a cross section of the ram head of FIG. 1.

[0015] In FIG. 1, 1 denotes a ram of a punch press machine which performs a reciprocal stroke movement in an upward and downward direction during press operation by means of a conventional driving source such as a hydraulic cylinder or the like. The lower end section of the ram 1 is formed as a mount seat 2 for a ram head 3, having a downwardly directed concave shape.

[0016] The ram head 3 has a striking section 3 a on the right in the example shown in the drawings, with an upper part formed in a joint section 3 b (FIG. 2) to be engaged in the downwardly directed concave mount seat 2. A plurality of bolt holes 3 c are formed in the ram head 3 for insertion of connection bolts 4 in a direction parallel to the stroke direction. The ram head 3 is connected to the mount seat 2 in the ram 1 by means of bolts 4 inserted in the holes 3 c.

[0017] Electrical insulation members 5 a and 5 b are disposed in the ram head 3 at an upper top end face and around the joint section 3 b with the ram 1, and electrical insulation members 6 a and 6 b for the bolts 4 are disposed at the side faced to a head 4a and a shaft 4 b of the bolts 4 in bolt holes 3 c in which the bolt 4 is to be inserted.

[0018] The ram head 3 is attached to the ram 1, namely to the machine side of the punch press machine, in an electrically insulated state, by engaging the ram head 3 to the mount seat 2 of the ram 1, driving a screw 4 c of the bolt 4 in a screw hole 2 a of the mount seat 2, positioning the aforementioned electrical insulation members 5 a, 5 b, 6 a and 6 b, and tightening the bolt 4.

[0019] In the present invention, an electrical conductive member, such as electric lead 8, is attached via a conductive bracket 7 of an inversed L-shape to a side (left side in the example of the drawing) of the aforementioned ram head 3 which has been provided in an electrically insulated state, and is designed so as to apply a direct current of 24V, as an example, to the lead 8. By so doing, when the bottom of the striking section 3 a of the ram head 3 is in contact with the top face of the punch tools 9 placed just under the ram head 3 at the return upward stop position of the punch tools 9 after operation, the current applied to the lead 8 is grounded to the punch press machine via the punch tools 9. Therefore, in the case where a detector (not shown) such as ampere meter is interposed between a power source (not shown) and the lead 8, the electric conduction, i.e., the contact between the ram head 3 and the punch tools 9 and the strip completion by the punch tools 9 are detected. If the ram head 3 and the punch tools 9 are not yet in contact, the current does not flow, and strip incompletion is detected. Further, even when the current is not detected immediately at the return upward stop position of the punch tools 9, it may be arbitrarily set to permit detecting of strip completion in the case where the current is detected within a predetermined period of time. Note that, in FIG. 1, reference numeral 10 denotes a holder (or turret) of the punch tools 9 and W denotes a work piece.

[0020] The present invention is as mentioned above, and when the punch press processing is performed by providing a ram head striking punch tools with its attachment area electrically insulated from the machine and applying a weak current to the ram head, the presence or absence of mis-stripping is determined by detecting contact or non-contact between the ram head and punch tools by the absence or flow of current. Therefore, there is no deviation of detection sensibility under the influence of vibration and impact, no damage to the sensor member by the punch tools rotation and no other problems such as are encountered by the conventional detecting methods in which an electric connection or an optical electric member functioning as a sensor is provided in the vicinity of the ram head by a post attachment structure. 

What is claimed is:
 1. A method for detecting mis-stripping in a punch press machine, comprising; operating a punch press having a ram head to strike a punch tool, the ram head being electrically insulated from the punch press machine; applying a weak current to the ram head, and determining the presence or absence of mis-stripping by detecting contact or non contact between said ram head and punch tool by detecting presence or absence of flow of said current.
 2. The method for detecting mis-stripping in a punch press machine as defined in claim 1 , wherein said weak current is a direct current of about 24V.
 3. A method for detecting mis-stripping in a punch press machine, comprising: providing a ram head of a punch press that is electrically insulated from the punch press machine; applying an electric current of low voltage to the ram head, at a return upward stop position of a punch tool, detecting grounding and conduction of the ram head to the machine through the punch tool when said ram head is in contact with the punch tool, and detecting non conduction when the ram head and the punch tool is not in contact, where the non conduction time is judged to be mis-stripping.
 4. The method of detecting mis-stripping in a punch press machine as defined in claim 3 , wherein said electric current is of about 24V.
 5. A detection apparatus for detecting mis-stripping in a punch press machine having a ram for contacting punch tools, comprising: a ram head having bores therethrough; fasteners passing through said bores and securing the ram head to the ram; electrical insulation disposed between the ram and the ram head; further electrical insulation disposed in the bores between the fasteners and the ram head; and an electrical conductive member conductively attached to the ram head; such that when the ram head contacts the punch tools an electric current supplied to the electrically conductive member will flow to the punch tools.
 6. A detection apparatus for detecting mis-stripping in a punch press machine having a ram for contacting punch tools as defined in claim 5 , wherein the fasteners are threaded bolts passing through the bores of the ram head and threadedly engaged in screw-holes in the ram.
 7. A detection apparatus for detecting mis-stripping in a punch press machine as defined in claim 6 , wherein the screw holes are provided in a concave mount seat of the ram and the ram head seats in said concave mount seat. 